This invention relates to a printing method and apparatus for printing by applying ink to a printing medium and, more particularly, to a printing method and apparatus for printing an image by transferring ink applied on an ink sheet to a printing medium.
Nowadays, as digital video cameras, digital cameras, and the like have become more prevalent, demand for color printers that print color images obtained by these apparatuses is increasing. One of printing methods of such color printers is a method of forming an ink image on a print sheet by selectively heating an ink sheet or ink ribbon applied with a thermal sublimation or hot-melt ink and applying (transferring) ink onto a printing medium.
Especially, a sublimation type thermal transfer printing apparatus can obtain high-quality full-color images, and is considered promising as a color printer for a digital camera.
As is known, an image printed using hot-melt ink is vulnerable to scratches. On the other hand, an image printed using thermal sublimation ink is easily deteriorated due to a fingerprint containing fats and oils, a plasticizer, and the like, and suffers color deterioration due to ultraviolet rays and re-sublimation due to heat. Hence, in order to protect a printed image, a so-called overcoat technique is known. In this technique, an overcoat layer is provided to an ink ribbon together with a color ink layer used to form an image, and after an ink image is transferred onto a printing sheet to form an image, the overcoat agent of the overcoat layer is transferred onto the printing sheet to form a protect layer on the image.
With this technique, an image obtained by the thermal transfer printing apparatus is environmentally and chemically tolerant, and is imparted with gloss, thus obtaining a high-quality, full-color image equivalent to a silver halide photo (photograph).
In the thermal transfer printing apparatus, since a printing sheet is reciprocally moved relative to a thermal head to print a plurality of color images, the printing sheet must be held upon printing images. Since margin portions where no image can be printed are formed on the printing sheet due to such mechanical limitation, an image cannot be printed on the entire surface of the printing sheet unlike a silver halide photo. However, some large-scale, business-use thermal transfer printing apparatuses use a printing sheet roll, and incorporate a cutter so as to realize the entire surface printing of a printing sheet. However, since such apparatus uses a sheet roll and incorporates a cutter, it is bulky and expensive.
In order to easily print an image on the entire surface of a printing sheet using a compact, inexpensive apparatus, a printing sheet having perforations as cut-off portions which are formed on the two sides of the printing sheet in the conveyance direction and allow the user to easily cut off margin portions is used, and an image is printed slightly larger than the finally required printing sheet size in which the margin portions are cut off at the perforations. After an image is printed, the margin portions are removed at the perforations to obtain a printed image which is printed on the entire surface of the printing sheet like a silver halide photo.
Using the overcoat technique and the printing technique on the entire surface of a printing sheet using perforations, even a compact, inexpensive thermal transfer printing apparatus can easily obtain a printed image, which is printed on the entire surface of the printing sheet like a silver halide photo, is environmentally and chemically tolerant and has a glossy appearance.
At this time, an image is normally printed slightly larger than the finally required printing sheet size in which margin portions are removed at perforations, taking print positioning accuracy in the printing apparatus into consideration, so that the printed image on the entire surface of a printing sheet can be consequently obtained. Also, an overcoat agent is applied to cover the entire printed image to form a protect layer that can sufficiently protect the printed image. Also, color ink transfer and overcoating of the overcoat agent onto a printing sheet are attained by the same method. In general, these processes are executed in the same sequence. As a result, the overcoat agent is also attached to the region of the printing sheet where the perforations are formed.
In this way, using the overcoat technique and the printing technique on the entire surface of a printing sheet using perforations, even a compact, inexpensive thermal transfer printing apparatus can easily obtain a printed image, which is printed on the entire surface of the printing sheet like a silver halide photo, is environmentally and chemically tolerant and has a glossy appearance.
However, in the prior art, in order to stably transfer an overcoat agent layer, optimal thermal transfer energy must be applied upon transfer, and a good bonding state between the printing sheet and overcoat layer must be obtained.
The perforations formed on the printing sheet are microscopically a plurality of holes (pores) forming a dotted line on the printing sheet, and portions around the holes that form the perforations on the surface of a printing sheet are roughened by the perforation forming process. Hence, the overcoat agent applied near the perforations of a printing sheet might not be stably transferred, and might readily peel since the agent is not satisfactorily transferred.
FIG. 8 is a sectional view and partial enlarged view of a print obtained by printing an image on a printing sheet in accordance with a conventional printing method. Referring to FIG. 8, reference numeral 21 denotes an overcoat layer formed by transferring an overcoat agent; and 22, perforations formed on the printing sheet.
Normally, an image printing region is covered by an overcoat region. In FIG. 8, the cross-hatched region corresponds to the image printing region, and the region where the overcoat agent is applied. Since a thin overcoat agent layer is formed to close the holes of the perforations, as shown in FIG. 8, this portion might be torn or cut off by a slight touch. Since the margin portions have to be cut off at the perforations to finally obtain a desired print, the overcoat layer formed around the perforations is torn off or peels anyway. In this manner, the overcoat layer formed around the perforations cannot be stably attached to the printing sheet, and is normally torn off or peels.
The overcoat layer (agent) that has been torn off or peeled becomes fine dust or powder dust, and is released into the environment where the printing apparatus is set. Such dust becomes contaminants for the printing apparatus, and may stain a print or cause image printing abnormality. Also, such fine or powder dust may pollute the environment where the apparatus is set.
Accordingly, it is an object of the present invention to provide a printing method and apparatus which can prevent an overcoat agent applied onto the surface of a printing medium for the purpose of protecting a printed image from being torn off or peeling from the printing medium, so that the overcoat agent will not become contaminants for the printing apparatus to stain a print, cause image printing abnormality, and become fine or powder dust in an environment.
According to one aspect of the present invention, the foregoing object is attained by providing a printing method for printing an image on a printing medium having cut-off portions that allow easy cutoff, comprising a printing step of printing an image by applying ink on the printing medium including the cut-off portions, and a protection layer forming step of forming a protection layer on the printing medium by applying a protection agent to a region, on the printing medium on which the image has been formed, except at least for the cut-off portions.
The printing step preferably includes the step of transferring and printing the image by frame-sequentially applying different color inks (e.g., yellow, magenta, and cyan inks) onto the printing medium using a thermal transfer printing method that uses an ink sheet applied with ink and prints by transferring the ink by heat energy.
According to another aspect of the present invention, the foregoing object is attained by providing a printing apparatus which uses a printhead for printing an image on a printing medium and prints an image on a printing medium having cut-off portions that allow easy cutoff, comprising printing means for printing an image by applying ink on the printing medium including the cut-off portions using the printhead, and protection layer forming means for forming a protection layer on the printing medium by applying a protection agent to a region, on the printing medium on which the image has been formed, except for the cut-off portions.
The printhead is preferably a thermal head having a linear array of a plurality of heating elements, and the ink and the protection agent are preferably applied on a sheet. Therefore, the printing means preferably heats the sheet using the thermal head and transfers the ink applied on the sheet to the printing medium, while the protection layer forming means preferably heats the sheet using the thermal head, and transfers the protection agent applied on the sheet to the printing medium.
Furthermore, the apparatus preferably further comprises conveyance means for conveying the printing medium, and the printing medium is preferably a printing paper sheet, which is formed with the cut-off portions at two end portions along a conveyance direction by the convey means.
When such printing sheet is used, the protection layer forming means can transfer the protection agent to avoid margins of the cut-off portions formed on the two end portions of the printing paper sheet, or can transfer the protection agent to a region of the printing paper sheet bounded by the cut-off portions while avoiding margins of the cut-off portions formed on the two end portions of the printing paper sheet.
Upon transferring the protection agent while conveying the printing medium by the conveyance means, a heat amount generated by the heating elements of the thermal head may gradually increase at the beginning of transfer of the protection agent, and may gradually decrease at the end of transfer of the protection agent.
In accordance with the present invention as described above, an image is printed on a printing medium, having cut-off portions that allow the user to easily cut off margin portions, by applying ink on a region including the cut-off portions on the printing medium, and a protection agent is applied to a region, except for the cut-off portion on the printing medium on which the image has been printed, to form a protection layer on the printing medium.
The invention is particularly advantageous when the margin portions are cut off from the printing medium at the cut-off portions, the protection layer formed on the printing medium can be prevented from peeling from the printing medium due to the cut-off portions, and a high-quality printed image can be stably preserved for a long period of time.
Since neither fine dust nor powder dust are produced due to the peeled protection layer, stain of a print, operation abnormality of the printing apparatus, and pollution of an environment where the apparatus is set owing to such dust can be prevented.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.